The present invention relates generally to hermetic scroll type compressors, and more particularly, to such a compressor having fixed and orbiting scroll members created by metal casting methods.
A typical scroll compressor comprises two facing scroll members, each having a wrap member, wherein the respective wraps are interfit to define a plurality of closed compression pockets. When one of the scroll members is orbited relative to the other, the pockets decrease in volume as they travel between a radially outer suction port and a radially inner discharge port, thereby conveying and compressing the refrigerant fluid.
A present problem with scroll members and that of associated scroll compressors is that of a lengthy wear-in or run-in time. Run-in time is the amount of time the compressor is required to be operated until the compressor mechanism reaches its designed efficiency rating. This run-in operation is inefficient, requiring the scroll compressor to be run-in at the purchaser's site after installation.
An additional problem exists with wear out of the scroll wraps. Uncompensated forces within the compressor can cause the scroll members to literally grind themselves together, leading to scroll members that are incapable of properly compressing fluid.
Prior attempts to solve the aforementioned problems comprised methods of creating a very hard scroll member or creating a scroll member having wrap tips having an even hardness. To create an even hardness over the scroll wrap tips, the inside scroll wrap sections were cast at a height greater than the outside wrap sections to create variable height wraps. Because of uneven cooling after casting, the variable height wraps of the casting caused the scroll member wrap member to form a flat, internal layer of substantially even hardness. By selectively milling portions of the scroll member, this layer of even hardness is brought to the surface so that it may wear against an opposing scroll member as is known in the art. If the wraps were cast even in height, after milling to a flat surface, the hardness would be uneven and this was considered undesirable.
The present invention solves the aforementioned problems providing a compressor with better run-in time and wear control by casting the scroll wraps level so that, when machined, the radially outer wraps are harder than the radially inner wraps.